L1-type cell adhesion molecules (CAM) are essential for proper nervous system development. We previously demonstrated that transsynaptic signaling of the sole invertebrate L1-type CAM neuroglian (Nrg) regulates synapse growth and stability and that its function in organizing the cytoskeleton at the synapse is conserved from flies to humans. Preliminary live imaging data reveals that in the adult Nrg is retrogradely transported from the synapse to the soma in a Lissencephaly 1 (Lis1)-dependent manner. This suggests that in the adult L1-type CAMs have a yet uncharacterized function that is distinct from its well-known developmental role at the plasma membrane. Retrogradely transported L1-type CAMs may be degraded or recycled in the soma, be part of a signaling endosome, or be retrograde signals themselves, which translocate to the nucleus. Recently, cytosolic 28kDa and 30KDa L1CAM fragments as well as a 70kDa transmembrane domain- containing fragment were shown to translocate to the nucleus. We have evidence that in addition to fragments, full-length Nrg translocates to the nuclei of Drosophila nervous systems and that Nrg fragments are likely to carry posttranslational modifications distinct from the full-length form. Our hypothesis s that some of the Nrg that is transported from the synapse to the soma will translocate to the nucleus. To test this, we will determine if the nuclear import of Nrg is reduced in Lis1 mutants when compared to wild type background and if the full- length Nrg form and its fragments carry different posttranslational modifications. In addition to nuclear translocation, we propose in aim 1 to determine mechanisms of L1-type CAM retrograde transport. We will use live imaging to determine the type of endosomal compartments in which axonal retrograde transport of Nrg occurs and the intracellular motifs that are required for Nrg retrograde transport. Recombinant expression of the intracellular domain (ICD) of L1CAM in non-neuronal cell lines altered the expression of genes involved in migration, cell cycle control and DNA damage checkpoint responses and in vitro experiments suggest that nuclear L1CAM may have a role in migration, neurite outgrowth and cellular protection against physical damage or genomic and oxidative stress caused by diseases or environmental influences. The main goal of aim 2 is to determine if nuclear L1-type CAMs have a functional role in vivo as well. For this, we will characterize the phenotypes of a mutant that lacks the transmembrane proximal nuclear localization sequence. In addition, we will transgenically express L1-type CAM proteins that mimic nuclear full- length L1-type protein and its fragments in the nervous system of Drosophila to determine if they have distinct functions by analyzing their induced phenotypes in vivo at the single cell and the organismal levels. In summary, the in vivo characterization of the mechanisms and functions of nuclear L1-type CAM signaling in the central nervous system will impact a broad range of research areas such as neuroprotection during stroke, spinal cord regeneration, Alzheimer's disease and cancer.